Composites Materials

Analysis of Composite Structures using ANSYS 12.0

and the ANSYS Composites PrepPost (ACP):

An Overview

Jean Paul Kabche, Ph.D.

Giovanni de Morais, M.Sc.

Maira Vargas, M.Sc.

Engineering Simulation Scientific Software (ESSS)

Presentation Outline

• Composite Materials Overview

• Composite Structures Modeling: General FEA Workflow

• Analysis of Composites with ANSYS Mechanical APDL• Analysis of Composites with ANSYS Mechanical APDL

• ANSYS Mechanical APDL: Composite Example

• ANSYS Mechanical APDL Limitations

• ANSYS Composites PrepPost: Introducing the ACP

Composite Materials: What are they?

Matrix: A homogenous base material that

forms the bulk of a composite material layer.

Fibers: Bonded or embedded reinforcing

fibers that are usually responsible for the

anisotropy of the composite.

Lamina: A composite material in sheet

form usually referred to as a layer or ply.

Laminate: A stack of lamina joined

together in arbitrary directions,

referred to as a composite lay-up.

anisotropy of the composite.

Longitudinal fiber direction

Transverse fiber direction

Composite Materials: Why use them?

• Benefits of composites

– High stiffness-to-mass ratio

– Corrosion resistant

– Adjustable thermal expansion properties

– Exceptional formability – Exceptional formability

– Outstanding durability

• Composite applications

– Aerospace

– Automotive

– Sporting goods

– Many, many others…

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Composite Structures Modeling: General FEA Workflow

Element Type Selection

Geometry Creation (lines, surfaces, volumes)

ANSYS DesignModeler

Third-Party CAD Software

Results Viewing

Pre-Processing Model Solution Post-Processing

Selection (beam, solid, shell)

ANSYS APDL

ANSYS Workbench

ANSYS Comp PrepPost

Layup Definition(thickness, angle, fiber

material, integration

points)

Failure Criteria Definition

(max strains, max

stresses)

ANSYS Structural Solvers

Mesh, Loads, BC

ANSYS Mechanical APDL

ANSYS WB Mechanical

ANSYS Comp PrepPost

Results Viewing(stresses, strains, interlaminar

shear stresses, safety margins, etc.)

Analysis of Composites with ANSYS Mechanical APDL

• At the global level (laminate) - Overall deflection

- Critical buckling loads

- Natural frequencies and mode shapes

• At the ply level • At the ply level - Interlaminar shear stresses

• At the matrix level - Stress distribution at matrix/fiber interfaces

• Failure of composites - Buckling of the structure (global level)

- Delamination (ply level)

- Fiber detachment (matrix level)


• Defining Composite Lay-ups >> Regular Shell Section

• A composite lay-up is

defined by inputting• Layer thickness

• Material ID (contains pre-• Material ID (contains pre-defined layer-wise material properties)

• Orientation (fiber angle with respect to a pre-defined reference coordinate system)

• Integration Pts (through-the-thickness integration points)


• Defining Composite Lay-ups >> Pre-integrated Shell Section

• A composite lay-up is

defined by inputting• Coefficients of the stiffness

matrices [A] [B] [D] are matrices [A] [B] [D] are computed outside of ANSYS Mech APDL and input into the Shell Section

• Recall that...• [A] = membrane stiffnesses

• [B] = coupling stiffnesses

• [D] = bending stiffnesses


• Element technology for composite modeling

– 1D: BEAM188/ BEAM189

– 2D: SHELL181/ SHELL281/ SHELL208/ SHELL209

– 3D: Layered SOLID185/ Layered SOLID186/ SOLSH190

• Failure criteria: has a layer failed due to the applied loads?

– Maximum Strain Failure Criterion: nine failure strains

– Maximum Stress Failure Criterion: nine failure stresses

– Tsai-Wu Failure Criterion: nine failure stresses and three additional coupling

coefficients

• Failure by interface delamination

– “Cohesive Zone Modeling” (CZM): specifies element separation laws

ANSYS Mechanical APDL: Composite Example

• Modal Analysis/ Buckling Analysis of a Composite Stiffened Section

• Compare the performance of SOLSH190 and SOLID186

Stringer Web

Compressive Load

Model 1: SOLSH190ANSYS 8-node Layered Solid-Shell

Model 2: SOLID186 ANSYS 20-node Layered Solid

Stringer Web

Skin

Stringer Flange

Fixed Support


• Results: Vertical Displacement (UZ) at 30 kN (first buckling load)

Model 1: SOLSH190ANSYS 8-node Layered Solid-Shell

Model 2: SOLID186ANSYS 20-node Layered Solid

Secondary Skin Buckling

Buckling Load = 30.6 kNBuckling Load = 31.6 kN


• Vertical skin displacement versus load

-1.00E+00

0.00E+00

SOLID186

SOLSH190

Primary skin buckling (~20 kN)

• Both elements predict the

buckling behavior well…

-7.00E+00

-6.00E+00

-5.00E+00

-4.00E+00

-3.00E+00

-2.00E+00

0.00E+00 2.00E+04 4.00E+04 6.00E+04 8.00E+04 1.00E+05 1.20E+05 1.40E+05 1.60E+05

Time

Va

lue

Secondary skin buckling (~30 kN)

Buckle crosses stringer web (~135 kN)

Applied Load (kN)

Ve

rtic

al D

isp

(mm

)However…

• SOLSH190 captures post-

buckling behavior

• SOLID186 results in solution

divergence after an applied load

of 135 kN

ANSYS Mechanical APDL Limitations

• The definition of layers can be very time-consuming

• Complex geometries may hinder layer definitions

• Numerous local coordinate systems required for fiber orientations• Numerous local coordinate systems required for fiber orientations

• Limited failure theories and the inability to combine different criteria

• Difficulty with model draping or woven fabric composites

• Limited post-processing capabilities

ANSYS Composites PrepPost: Introducing the ACP

• A new tool with advanced composites functionalities for pre- and post-processing of layered composite structures

• Provides seamless integration with ANSYS Workbench Mechanical and Mechanical APDLand Mechanical APDL

• ANSYS Structural solvers are used to compute solution

• Efficient definition of materials, orientations, plies and stacking sequences

• State-of-the-art failure criteria for composite structures

ACP: General Analysis Workflow

1) Mesh, loads and boundary conditions

are defined in ANSYS Mechanical APDL

or ANSYS WB Mechanical

2) ACP is launched from ANSYS WB

Mechanical or Mechanical APDL for

Model Tree

Python Scripting Interface

Main Window

Mechanical or Mechanical APDL for

composite material pre-processing

3) ACP generates an APDL file

4) Solution is computed using the

ANSYS solvers

5) Model results are imported into ACP

for post-processing

ACP: Material Definitions

Specify Layer Properties

Mo

de

l T

ree

Mo

de

l T

ree

• Basic engineering data used for finite element calculations

• Engineering constants (E1, E2, E3, G12, …, etc.)

• Failure criteria: strain limits, stress limits, Puck constants

ACP: Sub Laminate Definitions

Specify Layup Configuration

Mo

de

l T

ree

• Defines a sequence of layers with

different relative angles

Mo

de

l T

ree

different relative angles

• Each layer is assigned a set of

material properties

• Can be re-used in different areas

of the structure

ACP: Local Coordinate Systems for Fiber Orientation

Specify local systems for various regions of the model

Mo

de

l T

ree

Mo

de

l T

ree

• Definition of Cartesian, cylindrical and spherical systems

for fiber angle orientation definitions

ACP: Failure Analysis and Post-Processing

• Composite failure criteria is evaluated at all integration points of all layers of all elements requested

• Overlay text plot indicates critical • Overlay text plot indicates critical failure mode, critical layers and critical load case

• Definition of arbitrary failure criteria combinations

– Max. strain and stresses, Tsai-Wu, Tsai-

Hill, Hashin, LaRC

– Core failure and face sheet wrinkling for

sandwich structures

ACP: Failure Analysis and Post-Processing

• Failure criteria provided– Simple criteria (maximum stress) to

state-of-the-art (Puck criterion)

– Interlaminar shear and normal stresses

for shells

– Through-thickness failure for shells– Through-thickness failure for shells

– Combination of failure criteria

– Ability to create user-defined criteria

• Results displayed as– Critical failure criteria

– Critical layer

– Safety margins, reserve and inversed

reserve factors

Text plot highlighting critical failuremode, layers and load case

Composite Structure Analysis: Summary

• ANSYS Mechanical and Mechanical APDL are capable of analyzing composite structures using beam, shell and solid elements

• ANSYS’ composite material modeling and post-processing limitations are overcome by the ANSYS Composite PrepPost (ACP)are overcome by the ANSYS Composite PrepPost (ACP)

• ACP provides advanced composite pre- and post-processing capabilities which include: material definitions, layups, stackups, failure criteria, identification of critical failure mode, layer and load conditions

• ACP utilizes the ANSYS’ robust solvers to compute its base solution!

• ANSYS/ACP seamless integration will continue to progress in time!

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Composites Materials